Research spurs avian flu fears

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A duckling about to be killed by Chinese health workers during the February 2004 avian flu outbreak.Picture:Reuters

Scientists are investigating whether pigs could provide the "mixing vessel" for human and avian flu strains that would allow for deadly human-to-human transmission, as new outbreaks of avian flu virus appear in Thailand, China and Vietnam.

Professor Malik Peiris, a microbiologist at the University of Hong Kong, said the much-hyped human pandemic has not occurred yet because the virus has so far failed to readily make that human-to-human transmission.

"What is really important is you do not keep allowing this virus to try this on the human population, because then you increase the chance of that adaptation occurring," he said.

"For the poultry industry it is absolutely crucial (to bring it under control), and from the human health point of view."

The warning comes as the United Nations Food and Agriculture Organisation, which hosted a three-day international workshop on avian flu in Bangkok this week, supported the increased use of vaccines to control the virus. The FAO shift comes as new outbreaks of the H5N1 strain were confirmed in 12 Vietnamese provinces and 18 Thai provinces. It has also re-emerged in China.

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Dr Lawrence Gleeson, principal research scientist at the CSIRO's Animal Health Laboratory, in Bangkok for the meeting, said that "on balance" the flu still presented a risk.

"It is incumbent on animal health authorities to try to control this disease, to get the amount of the virus circulating in the poultry population down to a manageable level, so that the public health risk is simultaneously reduced," he said.

"If the transmission became as virulent in humans as it is in poultry, it would be absolutely horrific. In almost 50 per cent of cases reported the people have died."

Professor Peiris said scientists were carefully monitoring the role pigs could play in human-to-human transmission.

In research, he said, the human flu virus, H3N2, has been regularly found in pigs from China since 1998. In the US, quite independently, the human virus has jumped to pigs.

In this part of the world the human virus (in pigs) is still totally human, which is the worrying thing. PROFESSOR PEIRIS

"If you take human viruses and put them into a chicken it will not replicate: if you take an avian virus and put it in a human, it will not replicate most of the time," Professor Peiris said.

"There is a barrier: but both viruses will happily replicate in a pig, so that's why the hypothesis has been put forward that the pig could be the mixing vessel."

He said the virus probably started in ducks and then adapted to chickens, but it has not really adapted to any other mammalian species.

"Pigs are an important question mark, particularly with the pattern of backyard farming in this region where you have pigs together with poultry side by side," he said.

"In this part of the world the human virus (in pigs) is still totally human, which is the worrying thing. It provides this opportunity for the avian virus to mix its genes with the human virus and that is one of the ways previous pandemics have arisen. "Although there is no proof as to where the mixing occurred, the suspicion is it might have happened in a pig."